Humana Inc. (HUM), the second-biggest private provider of Medicare coverage, is no longer employing a law firm whose actions are being reviewed by a U.S. senator in connection with his probe into whether government information was leaked this month that sent insurers’ stock soaring. Humana cut its connections with Greenberg Traurig LLP after learning of the review, according to Tom Noland, a spokesman for the Louisville, Kentucky-based company. The insurance carrier also has begun an internal investigation, Noland said yesterday in a telephone interview. U.S. Senator Charles Grassley, an Iowa Republican, is reviewing whether an investor company, Height Analytics LLC, received inside information from a Greenberg Traurig employee before telling clients the afternoon of April 1 that officials would change plans and reduce a proposed rate cut for Medicare Advantage plans sold by private insurers.